A core research line at LENS concerns the study of ultracold quantum gases. By using suitable configurations of laser beams and magnetic fields it is possible to cool atomic gases down to few nanokelvin. At these ultra-low temperatures the atoms stop behaving as classical particles and their quantum nature emerges. If the particles are bosons they form a mesoscopic Bose-Einstein condensate (BEC), all collapsing into the same quantum state, while if they are fermions they form a Fermi-degenerate gas in which they completely fill all the lowest energy states available.

Quantum molecules

Interactions between atoms can be tuned by using static magnetic fields in proximity of so-called Feshbach resonances. The set of physical phenomena that can be studied by tuning intra- and inter-species interactions of atoms and mixtures in optical lattices is very large and ranges from the production of ultracold polar molecules to the engineering of novel quantum states of matter. The short-ranged isotropic interaction between atoms is indeed at the basis of superfluidity in Bose and Fermi systems, quantum phases in periodic and disordered potentials, entanglement. On the other hand, in a quantum gas of polar molecules a strong, tunable, long-range, anisotropic interaction appears, adding new ingredients to the study of superfluidity, quantum phase transitions, lattice models and quantum computation. Mixtures of different atoms that follow the two quantum statistics are also interesting to study a series of fundamental phenomena, ranging from condensed-matter to molecular physics.

Ultracold atoms trapped in optical lattices can be the material base for two kind of calculator: quantum computers and quantum simulators. In the first case, today's challenge at LENS concerns the ability to implement qubits, the basic elements of quantum information, on spin and/or electronic states of cold atoms (e.g. Itterbium) and to manipulate them one by one to perform calculations. In the second case, cold atoms in a optical lattices can show an electron-like behavior and allow an indirect study of conduction phenomena in condensed matter physics, such as superconductivity, Anderson localization, graphene properties and much more, thanks to the ability to draw very specific configurations of the lattices.

Cold atoms are the main ingredients of modern optical clocks, that can reach an accuracy of 10-18 seconds, against 10-15 s of atomic clocks. At LENS the research on optical clocks aims to simplify and reduce the size of the equipment to make them transportable, e.g. to send them in space. At lower temperatures, ultracold atoms in a condensed phase allow to perform atomic interferometry experiments and Strontium can be a useful quantum sensor to measure forces due to macroscopic source masses on micrometer distances, e.g. to investigate inverse-square Newton's law or Casimir effect.

Historically, high precision measurement of the Newtonian gravitational constant G has been done many times with various methods, such as torsion balance, torsion pendulum, beam balance and pendulum cavity, but always using suspended macroscopic masses. At LENS, Rubidium atoms in free fall will be used as probe masses to test the gravitational acceleration of nearby source masses, in a innovative experiment of atom interferometry that will allow a sensibility to a gradient up to 10-11 g. Moreover, the challenge of making portable this experimental apparatus is addressed.

In quantum simulation experiments, often the variables of the problem are encoded in internal states of the ultra-cold atoms. Using mixtures of two atomic species we can naturally store binary variables and using atomic interactions modulated by laser intensity to study the system behavior. With bosonic species as Rubidium 87 and Potassium 41 we are studying quantum magnetism, especially antiferromagnetic systems, and diffusion properties of atoms in several unidimensional lattices.

The goal of this research line is to develop a new generation of atomic sensors for the high precision measurement of gravity and accelerations. We plan to implement a Mach Zender interferometer with trapped Bose Einstein condensates with tunable interactions.
Negligible values of the inter-atomic scattering length will be used during the interferometric sequence in order to suppress undesired collisional shifts. Strong inter particle interactions will allow the generation of entangled states able to boost the sensitivity of the sensor beyond the standard quantum limit and to ideally reach the ultimate, Heisenberg, limit set by quantum mechanics. The resulting apparatus will show unprecedented spatial resolution and will compete with state-of-the-art interferometers with cold (non condensed) atomic gases.

One of the primary tools for handling ultra-cold atoms is the magnetic trap, which is needed both during cooling than during the experiment. In addition to macroscopic coils, it can be also possible to produce the necessary magnetic fields using the current circulating in a suitable gold and silicon chip a few inches from the side: an AtomChip. The benefits are higher frequencies of the trap at least an order of magnitude, ower evaporative time and a less stringent vacuum. Currently we study the behavior of the cloud of cold atoms, the goal is to make the best use of AtomChips in full quantum simulation experiments and in technological applications as quantum
memories.

We aim at studying two-dimensional fermionic 6Li atoms across the BCS-BEC crossover. We plan to benefit of the recent advances in ultracold atomic systems, such as single-site addressability and the full control of the interparticle interactions. Tailoring arbitrary optical potentials will create the perfect environment for implementing quantum models.
In particular, we want to characterize the superfluid phase by studying the interlayer tunneling, discriminating the coherent Josephson dynamics from the single-particle hopping.

By adding disorder we will simulate the physics of granular superconductors, testing the robustness of the order parameter and the onset of metallic phases at higher temperatures.

Laser spectroscopy of cold molecules is a powerful tool to address fundamental physical questions. We develop new methods to cool and control neutral molecules and apply them to improve the resolution of the spectroscopic measurements. In particular we exploit the Stark energy of polar molecules in non-homogeneous electric fields and use both conventional and microstructured devices to decelerate and trap cold molecules. Further, we develop novel narrow-linewidth light sources in the mid IR which are absolutely referenced to the primary frequency standard via a fibre-link to the National Metrological Institute in Torino, INRIM.

We aim at studying elusive superfluid and magnetic phenomena in a novel Fermi mixture of ultracold 6Li and 53Cr atoms. The peculiar Chromium-Lithium mass ratio uniquely enables a resonant control of three-body elastic interactions on top of the usual two-body ones, together with an extraordinary suppression of atom recombination into paired states in the regime of strong interspecies repulsion. The first property greatly enhances the observability of unconventional superfluidity, including Fulde-Ferrel-Larkin-Ovchinnikov phases and p-wave pairing. The second makes such mixture a prime platform for the quantum simulation of Stoner'
s model for itinerant ferromagnetism, hindered in nowadays experiments by the competing pairing instability.
We are finalizing the set-up of a new experimental machine which will benefit of high-resolution imaging of the system and state-of-the-art spectroscopy schemes, enabling a thorough investigation of the phase diagrams of Fermi-Fermi mixtures with attractive or repulsive interactions.

Funding (2015-2020): European Research Council Starting Grant: "Superfluidity and ferromagnetism of unequal mass fermions with two- and three-body resonant interactions ", PoLiChroM.

Ultracold atoms and trapped ions are among the most powerful tools to study quantum
physics. In our project, we plan to realize an atom-ion experiment of new generation in
which a quantum gas of fermionic Lithium and one or a few Barium ions coherently
interact. With this setup, we plan to investigate fundamental atom-ion interactions in the
ultracold regime, and to use these controlled interactions to realize a platform for
investigating out-of-equilibrium quantum systems and quantum thermodynamics.

Funding (ERC 2015-2020): European Research Council Starting Grant: "PlusOne"